In the conventional technology, an optical disk is generally manufactured by alternately laminating a dielectric body layer and a recording layer on a substrate (optical disk substrate) made from such a material as thermoplastic resin. In most cases, the optical disk as described above is manufactured with a film-formation apparatus based on the so-called sheet system which can form a film on a plurality of optical disk substrates respectively in batch.
Some of film-formation apparatus based on the sheet system and used for manufacturing optical disk substrates have a plurality of film-formation chambers in each of which film-formation is performed. In that case the film-formation chambers are linked to each other with one substrate carriage chamber. In the film-formation apparatus as described above, optical disk substrates once carried into the apparatus are successively carried through the substrate carriage chamber to each film-formation chamber, where a different type of dielectric body layer or a recording layer is formed and laminated, and then the substrate each with a film formed thereon are taken out to outside of the apparatus. With the film-formation apparatus as described above, a plurality of dielectric body layers or recording layers can be formed, which contributes to through-put in a film-formation step.
The film-formation chamber and substrate carriage chamber each in a film-formation apparatus are separated from each other with a substrate holder for holding an optical disk substrate on which a film is being formed. FIG. 42 shows a cross section of the substrate holder as described above.
The substrate holder 100 shown in FIG. 42 has a round support plate 35 on which an optical disk substrate 101 is placed, and an arm section 37 for holding the support plate 35. Provided on the support plate 35 are an inner mask 38 which fixes an optical disk substrate 101 at a position close to its center (described as fixing section A) and an outer mask 39 which fixes the optical disk substrate 101 at a position close to its peripheral section (described as fixing section B). As shown in this figure, the optical disk substrate 101 is held and fixed between the inner mask 38 and outer mask 39.
The substrate holder 100 fixes the optical disk substrate 101 in such a way that the fixing section A and fixing section B contact the support plate 35 and there is a clearance a between other portion and the support plate 35. Thus, the optical disk substrate 101 can easily be removed from the support plate 35, which prevents the optical disk from being broken when removed from the support plate 35.
In recent years, there is the strong need for enlarging a recording capacity of an optical disk from 650 MB to 4.7 GB. To satisfy this need, there is the technology of adhering two optical disks to each other so that data can be recorded on both sides of the optical disk. In this type of optical disk based on the adhesion system, it is necessary to reduce the thickness of the optical disk from 1.2 mm like in the conventional technology to 0.6 mm. When the optical disk substrate is thin, naturally the mechanical and thermal strength decreases. When the thermal strength lower, the optical disk gets deformed during the film formation, and number of conceivably defective products which do not satisfy the requirements increases. This problem is especially serious when it is tried to maintain a through-put in the film formation step as that in the conventional technology.
In an optical disk (optical recording disk), a data recording section which can optically record and reproduce data is provided on a substrate, and the optical disk is used as a disk for filing documents or data therein. When the optical disk is used, the disk is rotated at a high speed, and a laser beam focused to a diameter of around 1 μm is irradiated thereon, and data is read out from the recording layer or data is recorded in the recording layer executing focus adjustment and positional detection.
When manufacturing various types of optical disk media, a step of forming a reflection layer, a recording layer, a dielectric body layer, or a protection layer by sputtering is indispensable. In film formation by sputtering, Ar plasma or the like is generated in a vacuum, a surface of a target is hit by ions in this plasma, and a film is piled up on an opposite substrate, so that heat is inevitably generated during film formation by sputtering. In the optical disk, generally a polymeric material such as polycarbonate is used as a material for a disk substrate, so that temperature increase in the film-formation chamber may sometimes cause deformation of the disk substrate. This problem becomes especially serious when film formation is continuously executed at a high speed, when a thick film is formed, or when two or more layers are repeatedly formed on the same substrate, and is still further series when the method is applied to manufacture a thin substrate with a thickness of 0.6 mm used in the DVD media.
To solve the problem described above, for instance, Japanese Patent Laid-Open Publication No. HEI 10-81964 (Title of the Invention: Sputter Holder for an Optical Recording Medium and Optical Recording Medium Manufacture Method) proposes a sputter device for manufacturing an optical recording medium, in which a sputter holder (substrate holder) for holding a substrate on which a film is to be formed having different heights in the outer section and inner sections each contacting a substrate is provided, a substrate is placed on this substrate holder, and deformation of the substrate is reduced by executing sputter film-formation in a state where the substrate is bent in a direction reverse to that in which the substrate is bent-during film-formation by sputtering.
Further in the conventional technology, when a plane substrate is loaded on a substrate holder of a vacuum film-formation apparatus (an optical disk substrate film-formation apparatus) for film formation to manufacture an optical disk, gas in a clearance between a rear surface of the substrate and the substrate holder is hardly evaluated to a vacuum state, and a time required to evaluate the gas down to a prespecified pressure level may be disadvantageously long. In addition, when a substrate with a film having been formed is carried out from the film-formation apparatus, sometimes the substrate is kept in a state where the substrate is vacuum-adsorbed to the substrate holder and is hardly separated from the substrate holder, which causes troubles in operations for taking out and carrying the substrate.
To solve the problem described above, for instance, Japanese Patent Laid-Open Publication No. HEI 2-273345 discloses a holder based on a structure in which an evacuation hole is provided in a recording medium substrate holder. Further, Japanese Utility Model Laid-Open Publication No. HEI 4-137526 discloses a holder based on a structure in which a gas evacuation hole is provided in a recording medium substrate holder as well as a substrate holder (opposite to a recording surface). In these conventional technologies, it is tried to evacuate gas on a rear surface of a substrate and to prevent adsorption of a substrate by providing a gas evacuation hole in a substrate holder.
In recent years, an optical disk making use of phase-change is often used as a rewritable optical disk. Generally the phase-change recording type of optical disk comprises a transparent plastic substrate on which convex and concave sections are provided at an arbitrary pitch, a lower dielectric body protection layer using ZnS—Si2 as a dielectric material, a phase-change recording layer using a chalcogen-based recording material such as GeSbTe, InSbTe, or AgInSbTe, an upper dielectric body protection layer made from ZnS—SiO2 like in the lower dielectric body protection layer, and a reflection/heat-emission layer using mainly an Al-based alloy, Au, or Ag, and each of the layers is also formed by sputtering.
In Japanese Patent Laid-Open Publication No. HEI 10-8964, however, warping in a radial direction of a substrate is taken into considerations, but there is no countermeasures against the mechanical characteristics of the substrate in a peripheral direction of the substrate, and when viewed totally, countermeasures against deformation of a substrate which occurs during film formation by sputtering is not always appropriate.
For instance, in production of DVD media, generally a film is formed by sputtering on a substrate having a thickness of 0.6 mm, and then a blank substrate having a thickness of 0.6 mm is adhered to the former substrate. As it is difficult to correct warping of a substrate in the peripheral direction in the adhesion step, it is essential to suppress warping of a substrate in the peripheral direction during film formation by sputtering, but this objective has not successfully been achieved in the conventional technology.
With the inventions disclosed in Japanese Patent Laid-Open Publication No. HEI 2-273345 or in Japanese Utility Model Laid Open Publication No. HEI 4-137526, although it is possible to prevent vacuum adsorption when taking out a substrate from a substrate holder, in a case of substrate made from a plastic material, when incident energy from particles sputtered during film formation is accumulated, temperature of the substrate easily rises due to accumulation of heat in the substrate made from the plastic material, and if a groove for preventing vacuum adsorption is formed on a surface of a holder closely contacting a rear surface of a substrate, difference between temperature in the closely contacting section and that in the groove section is generated, and a new problem of thermal deformation of a substrate occurs.
As described above, in the case of a substrate made from a plastic material, sometimes incident thermal energy may negatively affect the mechanical precision of the substrate. Especially when fine bits like those in an optical disk are formed on a surface, lowering of the mechanical precision due to deformation causes big troubles in recording, reading, or deleting data. Further, in production of various types of optical disk, a step of forming a reflection layer, a recording layer, a dielectric body layer, and a protection layer with a sputter device continuously and successively at a high speed is indispensable, so that the introduced thermal energy is easily accumulated. Especially, when a thin substrate having a thickness of 0.6 mm like a DVD media substrate is used, thermal deformation easily occurs, so that this problem is extremely serious in relation to maintenance of the mechanical precision.
When a trouble occurs due to thermal deformation of a substrate or for some other reasons while the substrate is being carried, it not only causes a failure of the device, but also extremely lowers the productivity of the production facility, which may in turn causes cost increase, and lowering of productivity or the like. Further, when the vacuum adsorption occurs in a step of taking out a substrate from a substrate holder, even if the substrate can be separated from the substrate holder in the carriage system side, scratches or other damages may be generated on a rear surface of the substrate, which in turns lowers the production yield, and further it may cause a serious problem in realization of a substrate carriage process at a higher speed.
In the case of phase-change recording type of optical disk, when it is tried to raise power for sputtering in film formation, temperature of the substrate remarkably rises, which causes warping of the substrate with reproduction of recorded data disabled. A recording disk based on a DVD system with a small thickness is especially weak to heat.
Japanese Patent Laid-Open Publication No. HEI 10-162435 discloses an invention relating to a reflection layer in a phase-change recording type of optical disk, and in this invention a mixture of Mg and Ag or the like is used for the reflection layer to improve the repetition performance.